The present invention relates to an airborne or ground station. An airborne or ground station of this kind is known from German Published Patent Application (DT-OS) 2,038,982. DME and TACAN airborne or ground stations per se are described in a book by E. Kramar, "Funksysteme fur Ortung und Navigation", published by Berliner Union GmbH, Stuttgart 1973, pages 147 to 169.
In DT-OS 2,038,982, a direction finder co-located with the DME transponder determines the angle of arrival of the DME interrogation signal, and this angle value is transmitted together with the DME reply signal to the interrogator in coded form. As possible coding methods, the application proposes phase modulation, amplitude modulation or pulse-spacing modulation. With pulse-spacing modulation, the angle information is contained in the space between an additional pulse pair and the DME reply pulse pair. That proposal has been implemented in the new microwave landing system DLS, which is generally known from the literature.
Consideration has also been given to the possibility of implementing the information transmission by modulating the phase of the carrier wave of the pulses. In the known phase modulations, however, the predetermined bandwidth of a DME/TACAN channel is exceeded, so it is not permissible in the existing systems. The bandwidth is laid down by, e.g., the "International Standards and Recommended Practices, Aeronautical Telecommunications, Annex 10 to the Convention on International Civil Aviation". Thus, the known phase modulation will only be applicable in new navigation systems whose bandwidths have not been fixed yet.